Interpretive Summary: Cotton producers are faced with many choices including cotton varieties, herbicide systems, tillage systems, and row spacings. Researchers from the National Soil Dynamics Laboratory and cooperators from the Agronomy and Soils Department at Auburn University compared a conventional variety, a Roundup Ready® variety, and a Liberty-Link® variety in both conventional tillage and conservation tillage systems for standard row (40-inch) and narrow row (15-inch) cotton planting patterns. The experiment was conducted during the 2004-2006 growing seasons at the E.V. Smith Research Center, Field Crops Unit near Shorter, AL. Data collection included plant populations, lint yields, and plant biomass at 1st square and mid-bloom. Plant populations were 22% higher for 15-inch cotton compared to 40-inch cotton, but this could be attributed to a higher initial seeding rate in 15-inch cotton plots. Lint yields were influenced more by the growing season than row spacing, variety, or tillage system. Plant biomass measured at 1st square and mid-bloom was also affected by growing season with 15-inch cotton plant biomass averaging 34% greater in 2004 and 2005. Although 15-inch lint yields were equivalent to 40-inch cotton lint yields, an extensive economic analysis is required to account for differing plant populations, technology fees, tillage systems, and herbicide systems.

Technical Abstract:
Cotton producers are faced with a myriad of choices including cotton varieties, herbicide systems, tillage systems, and row spacings. A study was conducted to compare a conventional variety, a glyphosate tolerant variety, and a glufosinate tolerant variety in both conventional tillage and conservation tillage systems for standard row (40-inch) and narrow row (15-inch) cotton planting patterns. The experiment was conducted during the 2004-2006 growing seasons at the E.V. Smith Research Center, Field Crops Unit near Shorter, AL. Data collection included plant populations, lint yields, and plant biomass at 1st square and mid-bloom. Plant populations were 22% higher for 15-inch cotton compared to 40-inch cotton, reflecting a 35% higher seeding rate in 15-inch cotton plots. Lint yields were influenced more by the growing season than row spacing, variety, or tillage system. Plant biomass measured at 1st square and mid-bloom were also affected by growing season with 15-inch cotton plant biomass averaging 34% greater in 2004 and 2005, however, the effect of tillage system was contradictory during the same growing seasons. The 15-inch lint yields were equivalent to 40-inch cotton lint yields, while plant biomass was greater for 15-inch cotton at both growth stages. An extensive economic analysis is required to account for differing plant populations, technology fees, tillage systems, and herbicide systems to determine if a 15-inch system is more profitable than a traditional cotton system with wider row spacings.